IN-SITU THERMAL REMEDIATION OF TRICHLOROETHENE USING SIX-PHASE HEATING AT THE PADUCAH GASEOUS DIFFUSION PLANT, PADUCAH, KENTUCKY

The Six-Phase Heating (SPH) treatability study was conducted under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This treatability study has provided quantitative treatment and cost data to assess the feasibility of deploying electrical resistance heating technology as a part of the remedial action for the Groundwater Operable Unit at the Paducah Gaseous Diffusion Plant (PGDP). Operation of the system began on February 14, 2003 and the system was shut down September 6, 2003. The SPH treatability study was implemented at the U.S. Department of Energy’s PGDP located in Paducah, Kentucky. The primary objective of the treatability study was to demonstrate the implementation of this technology for the remediation of trichloroethene (TCE) and associated volatile organic compounds (VOC) in the unsaturated and saturated zones of the Upper Continental Recharge System (UCRS) and the groundwater of the Regional Gravel Aquifer (RGA). The presence of dense non-aqueous phase liquids in the groundwater are believed to be one of the major sources of TCE feeding the contaminated plume located beneath the site. Execution of the SPH treatability study included the installation and operation of one SPH array. The single array consists of six power electrodes, a center neutral electrode, a power control unit, a steam and contaminant vapor recovery (VR) system, pressure and temperature monitoring systems, and contaminant vapor and water treatment systems. During operation, as the electrodes heat the subsurface, volatile organics and groundwater are converted to a vapor phase. The vapors migrate upward to be recovered by VR wells and steam vents constructed within the electrode borings and by the steam vents located in vacuum monitoring piezometer borings. Captured vapors and steam are evacuated to the surface where the steam is condensed and the vapors are adsorbed onto granulated carbon filters. The removal of TCE in the groundwater of the RGA was assessed by a comparison of baseline groundwater sample results to post treatment groundwater sampling results. The post treatment groundwater sample results as compared to the baseline groundwater sample results indicate a 99 percent reduction in TCE concentration in groundwater. The removal of TCE in the UCRS soil was also assessed by a comparison of the baseline soil sample results to the post treatment soil sample results. This comparison indicates an average TCE concentration reduction in soil of 98 percent.